package javax.servlet;

import java.io.IOException;

/**
 *
 * 在服务器上定义接收和发送requests的对象
 *
 * Defines an object that receives requests from the client
 * and sends them to any resource (such as a servlet,
 * HTML file, or JSP file) on the server. The servlet
 * container creates the <code>RequestDispatcher</code> object,
 * which is used as a wrapper around a server resource located
 * at a particular path or given by a particular name.
 *
 * <p>This interface is intended to wrap servlets,
 * but a servlet container can create <code>RequestDispatcher</code>
 * objects to wrap any type of resource.
 *
 * @see ServletContext#getRequestDispatcher(java.lang.String)
 * @see ServletContext#getNamedDispatcher(java.lang.String)
 * @see ServletRequest#getRequestDispatcher(java.lang.String)
 *
 * @version $Rev: 467553 $ $Date: 2006-10-24 21:01:51 -0700 (Tue, 24 Oct 2006) $
 */
public interface RequestDispatcher {
    /**
     *
     * 请求转发
     *
     * Forwards a request from
     * a servlet to another resource (servlet, JSP file, or
     * HTML file) on the server. This method allows
     * one servlet to do preliminary processing of
     * a request and another resource to generate
     * the response.
     *
     * <p>For a <code>RequestDispatcher</code> obtained via
     * <code>getRequestDispatcher()</code>, the <code>ServletRequest</code>
     * object has its path elements and parameters adjusted to match
     * the path of the target resource.
     *
     * <p><code>forward</code> should be called before the response has been
     * committed to the client (before response body output has been flushed).
     * If the response already has been committed, this method throws
     * an <code>IllegalStateException</code>.
     * Uncommitted output in the response buffer is automatically cleared
     * before the forward.
     *
     * <p>The request and response parameters must be either the same
     * objects as were passed to the calling servlet's service method or be
     * subclasses of the {@link ServletRequestWrapper} or {@link ServletResponseWrapper} classes
     * that wrap them.
     *
     *
     * @param request a {@link ServletRequest} object
     * that represents the request the client makes of the servlet
     *
     * @param response a {@link ServletResponse} object
     * that represents the response the servlet returns to the client
     *
     * @exception ServletException if the target resource throws this exception
     *
     * @exception IOException if the target resource throws this exception
     *
     * @exception IllegalStateException if the response was already committed
     */
    public void forward(ServletRequest request, ServletResponse response)
            throws ServletException, IOException;

    /**
     *
     * jsp中的include
     *
     * Includes the content of a resource (servlet, JSP page,
     * HTML file) in the response. In essence, this method enables
     * programmatic server-side includes.
     *
     * <p>The {@link ServletResponse} object has its path elements
     * and parameters remain unchanged from the caller's. The included
     * servlet cannot change the response status code or set headers;
     * any attempt to make a change is ignored.
     *
     * <p>The request and response parameters must be either the same
     * objects as were passed to the calling servlet's service method or be
     * subclasses of the {@link ServletRequestWrapper} or {@link ServletResponseWrapper} classes
     * that wrap them.
     *
     * @param request a {@link ServletRequest} object
     * that contains the client's request
     *
     * @param response a {@link ServletResponse} object
     * that contains the servlet's response
     *
     * @exception ServletException if the included resource throws this exception
     *
     * @exception IOException if the included resource throws this exception
     */
    public void include(ServletRequest request, ServletResponse response)
            throws ServletException, IOException;
}








